Can Nasa Actually Defend Us From An Asteroid?

On October 12 an asteroid the size of a house, moving 9 times faster than a bullet, flew past Earth at a distance closer than the Moon.

Although this asteroid posed no threat, NASA had been watching it closely ever since it was discovered. They were using its close proximity to test their newly established planetary defense network.

This is a global network of government agencies, observatories, academic institutions, and amateur astronomers.

And they are all that stand between us and an asteroid impact.

But could NASA actually defend us against an approaching asteroid?

But if you happened to look up at the sky on October 12, you wouldn’t be able to see it. It was invisible to the naked eye.

Asteroid 2012 TC4 wasn’t going to hit the Earth. It missed by almost 40,000 kilometers — a close shave by astronomical standards but far enough we needn’t be worried.

Afterall, an asteroid of that size hits the Earth about every 60 years. It’s truly a once in a lifetime event.

But a similar-sized rock slammed into the atmosphere near the Russian city of Chelyabinsk just 4 years ago.

It burned up before ever reaching the ground, producing a fireball brighter than the Sun. It could be seen for hundreds of kilometers and exploded with the force of an atomic bomb. The shock wave broke windows, damaging over 7000 buildings and injuring over a thousand people.

And no one ever saw it coming.

Granted, it’s exceedingly hard to spot these asteroids. Space is big and these rocks are tiny in comparison.

But to survey such a large section of the sky for tiny dark — practically invisible — lumps of rock is a huge undertaking. One that cannot be tackled by a single person — or even a single institution. If the need to defend the planet from an oncoming asteroid ever became apparent, it would require the efforts of telescopes all around the world from multiple nations, requiring the expertise of people from all kinds of backgrounds and disciplines.

In order to spot these rocks, we need eyes on the sky all around the globe. That means using ground and space-based telescopes from a variety of institutions — not just NASA. The Planetary Defense Coordination Office is responsible for detecting, cataloguing, and tracking Near Earth Objects. And if any appear to be a threat to the Earth, the Planetary Defense Coordination Office would organize the efforts to mitigate or stop a space rock from impacting the Earth.

At this very moment, over a thousand potentially hazardous asteroids are hanging over our heads. To clinch the distinguished title of potentially hazardous, an asteroid must be on a trajectory that could someday put it on a collision course with Earth — and be big enough to cause some damage. That usually means somewhere above 100 meters in diameter — larger than a football field.

An asteroid that size only hits the Earth on average every few thousand years. But when they do, they can cause as much destruction as a thermonuclear weapon.

In 1908, an object of this size hit Siberia, near the Stony Tunguska River. It leveled 2000 square kilometers of forest and knocked people off their feet hundreds of kilometers away. Luckily, the impact occurred in a mostly uninhabited area of the planet. The victims were mostly trees. If it had hit closer to a city, the destruction would have been catastrophic.

Again, no one saw this coming. No one was even looking at the time.

Since the detection and deflection of an oncoming hazardous asteroid would require the coordinated effort of so many disparate governments and institutions, we can’t wait for a hazardous asteroid on a collision course to suddenly appear. By then it would be far too late.

So as this house-sized boulder crossed the sky at 14 kilometers per second, NASA’s Planetary Defense Coordination Office conducted a practice run of what would do if it ever had to deal with an oncoming asteroid.

Since 1998, NASA has made it their goal to catalogue at least 90% of the asteroids and comets close enough and large enough to threaten the planet. That means rocks that cross Earth’s orbit and are 1 kilometer or larger.

An impact event with a rock that size would be a global catastrophe unlike anything ever experienced in recorded history. The fallout from such an event would wreak havoc on global ecosystems, leading to mass extinctions — possibly our own.

In the time since NASA began cataloging these space rocks, astronomers have met and exceeded that goal. But that doesn’t mean they are done. There are still many rocks out there waiting to be discovered, and with the ones they have discovered, their orbits need to be calculated and refined.

This requires constant observation. The more they can observe an asteroid, the greater they can refine its orbit. And knowing its orbit is the only way we can know if it is on a collision course or not.

NASA — along with partners around the world — have been monitoring today’s asteroid since its detection in 2012. With each observation, they’ve been able to fine-tune their understanding of its size and trajectory, giving them a better picture of just where exactly it will be today.

Early observations of an object’s orbit are only be able to give the probability of an impact. As more observations are made and the object’s orbit is better understood, the probability of impact will either increase or decrease. Usually after constant monitoring and further observations, the probability of impact shrinks to zero.

But not before rising usually.

Because the more we observe an object’s movements, the better we understand its orbit. At first, the projections of an object’s position in the future are full of uncertainty. That means it’s future position isn’t fixed. It could be in a number of places and if you add up all the possible trajectories, it’s position at any given moment in the future becomes an array of possibilities that occupy a huge band of space. For it to be any danger to us, the Earth must fall within that band of space where the object might be. At first this band is huge, occupying a large swath of space, because our uncertainty of its orbit is huge. As we refine its orbit, the band shrinks and the object’s future position is narrowed down. If the Earth remains inside of this band as it shrinks, the odds of impact increase. And they will continue to increase as long as Earth stays there.

Once we fall outside of it, the odds drop to zero.

But sometimes that doesn’t happen.

In 2008, a car-sized meteor was spotted by the Catalina Sky Survey telescope. Astronomers there determined that it was on a collision course with the Earth and correctly predicted the location and time of its impact. Since the rock was only the size an oldsmobile, it didn’t pose a threat and it burned up in the atmosphere.

We have two scales we use when assessing the threat of an asteroid impact.

The Torino Scale is simpler and meant for communication with the public. It uses a scale from 0 to 10 based on the probability that an object will hit and the size of the object. 0 means the object is small and has basically no chance of hitting the Earth. A 10 will almost certainly hit the Earth and it is big enough to inflict global disaster.

The Palermo Scale is more complicated but essentially measures the same thing. It is a logarithmic scale so every increase above zero means an order of magnitude increase in the risk of impact.

In 2004, the asteroid Apophis set the record for highest risk assessment on both the Palermo and Torino scales. For a brief period, Apophis held a 4 value on the Torino scale and a 1.10 value on the Palermo, meaning it was 12.6 times more likely than average to impact the Earth in the year 2029. But Further observations ruled out the chance of impact.

But if Apophis had continued on a collision course, then the Planetary Defense Coordination Office would have to start thinking about deflection efforts.

This has never happened before.

But NASA and researchers around the world have put a lot of thought into how you could stop a mountain-sized rock moving faster than a bullet.

A rock that size just has too much mass, too much momentum to be completely stopped.

But you can nudge it. And that might be enough.

The Earth is moving at about 30km a sec in its orbit around the Sun. That means it moves its entire width through space in about 7 minutes. If an asteroid headed on a collision course were delayed or advanced by 7 minutes, it would miss the Earth entirely.

Now you can do this in a couple ways.

The simplest and cheapest method would be to launch missiles at the object. These could be nuclear bombs or merely a bunch of cannonballs thrown in the asteroid’s path. Either way the goal would be to impart enough kinetic energy into the object to slow it down just enough that it would be late for its scheduled impact with the Earth.

Nuclear weapons are the most familiar method of asteroid deflection because they are always used in the movies but nukes aren’t the only way and they’re not necessarily the best way to deflect an asteroid. And in some ways, nukes may be one of the more boring ways to save the Earth from an oncoming asteroid.

In 2005, NASA crashed a space probe into the comet Tempel 1 — on purpose. Dubbed Deep Impact, the intended mission was to study the interior composition of the comet but the impact altered the comet’s orbit by around 10 meters. A relatively modest change but the Deep Impact mission serves as a proof of concept that we could nudge an asteroid out of the way just by crashing into it.

Or you could attach conventional rocket engines to the object and turn it into massive, incredibly slow moving spaceship.

But that only really works if the object is a solid mass of material. Many asteroids might just be big conglomerations of loose rock. Basically, piles of rubble leftover from the birth of the solar system. Bombing such an object might disrupt the pile but not change its trajectory much. So nuclear weapons are off the table. And it would be hard to afix rocket engines to what is essentially a big floating cloud of gravel.

But we wouldn’t even need to come into contact with the object necessarily to move it. A spacecraft could be put into orbit around the object — whether its solid or not. The gravitational attraction between the craft and the asteroid would slowly push the asteroid onto another course.

This is called a gravity tractor. It would be very slow, requiring years, even decades to alter an asteroid’s trajectory enough to make it harmless.

Given enough lead time though, seemingly small alterations in the object’s orbit could lead to big changes down the line.

For instance, painting an asteroid bright white might be enough to change its orbit. The white paint job would increase the Sun’s reflective radiation pressure on it, effectively pushing the asteroid onto a new course using sunlight alone.

Or you could paint it black, making it absorb more of the Sun’s energy, and using the increased emission of thermal radiation to move an entire mountain of rock.

Or you could deflect it with a cloud. Putting a cloud of water vapor in the path of the asteroid might provide just enough friction to slow the object down and make it miss the Earth.

We’d need decades of advance warning. That means we need as many eyes on the sky as possible. All the way from the big telescopes like the aptly named Very Large Telescope in the Atacama Desert to amateur astronomers in their backyards.

In the time since the Tunguska Event, we’ve become increasingly aware of the interplanetary shooting gallery that the Earth exists within. Evidence of great impacts in the past scar the surface of our planet. And as our surveillance of the sky grows, the more potentially hazardous objects we become aware of.

Despite the ever increasing number of potentially hazardous objects, the odds of being hit by one on any given day are extremely small. But one thing is certain: someday we will be hit by an asteroid or a comet. Without a concerted and coordinated effort to detect and track these objects, we have no way of knowing for sure when.

But if a dangerous asteroid were detected tomorrow, we would have nothing ready to stop it. All the deflection ideas I just talked about remain just that: ideas. Relegated to academic papers and intellectual exercises.

It could take years — even decades — just to get any of these ideas out of the realm of theory and into space.

There is a proposed mission to test out the feasibility of redirecting an asteroid. Called the Asteroid Impact and Deflection Assessment or AIDA, the mission would send two spacecraft to Didymos, an asteroid with its own moon. One spacecraft would impact the moon while the other would measure the effects. If all goes well, the impactor spacecraft will be able to nudge the asteroid’s moon a bit, proving that we could deflect an asteroid if necessary.

But the mission has not been able to secure funding, and whether or not it’ll actually happen is uncertain.

It is currently our only line of defense. We need to be able to detect them long before they become a danger.

NASA’s Planetary Defense office is a young agency. It was only established in January of 2016. Needless to say, the odds are against them. But each asteroid that comes within range of our telescopes gives us another chance to refine our techniques, reduce the uncertainty of our projections, and increase our odds.

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